This invention pertains to the art of cooking appliances and, more particularly, to an oven for cooking a food product by air alone; or a combination of air and microwave energy. The invention has particular application to high speed cooking of food products at very high quality standards.
Restaurants and commercial cooking establishments have a need for faster cooked food in order to more efficiently run and maintain their commercial businesses. The ability to more rapidly cook food, and thereby more quickly serve food and move customers through a restaurant has great value during peak times when table space may limited due to high customer traffic. Therefore, speed cooking ovens are becoming more widely known and utilized by those skilled in the art of commercial cooking. There exist several types of commercial speed cooking ovens on the market today. These commercial cooking ovens utilize various techniques to accomplish speed cooking and have been and are referred to herein as “hybrid” ovens, and are generally defined as ovens that employ a combination of microwave energy and at least one other thermal source (convection, radiant energy, and/or steam) to increase cooking speed over a conventional oven, while at the same time maintaining a quality of cooking reasonably similar to a conventional cooking oven. As used herein the terms “hybrid” and “combination” have the same meaning unless otherwise specified and the terms “conventional cooking oven” “conventional cooking” and “conventional means”, have the same meaning and refer to cooking at the quality level and at the speed that is currently widely utilized. By way of example, the “conventional cooking time” for a brand name of Grand Cinnamon rolls, according to the package, is approximately 28–30 minutes (e.g. conventional cooking time).
Just as speed cooking will become the standard for commercial cooking, speed cooking also has application in residential cooking, and will become the standard for residential use also. The ability to quickly cook food, and the ability to cook a variety of food products together without flavor or odor transfer from one food product to the next, within the same cooking operation, is desirable and of high interest to residential as well as commercial users.
There have been relatively few dramatic changes in the cooking art over the years, as man has moved from open flame cooking at the campfire to gas fired and electric resistance heating elements for cooking; and later the introduction of the microwave oven totally revolutionized the food industry as new food products were developed, new methods of food distribution developed and new and different opportunities opened up for residential and commercial establishments as re-thermalization of food products, very quickly, became possible. It is not necessary to recount the dynamic impact the introduction of the microwave has had on daily life, and also the many industries that were created because of the introduction of affordable microwave re-heating devices.
High quality speed cooking will become the next standard as people will want the ability to cook very quickly, but also will want a high quality food product. It is always therefore very important that speed cooking produces a finished food product that is at least as good as conventionally cooked food products, and in some cases as high as gourmet standards. For example, a frozen pizza can be cooked in just 3 minutes or less in a speed cooking oven as compared to the conventional cooking time of approximately 25–30 minutes in a conventional oven. Or, cinnamon rolls cooked from raw dough can be cooked in a speed cooking oven in 2–3 minutes instead of the conventional 28–30 minutes. Each food product can be cooked at these speeds and maintain the taste appearance and overall quality of a conventionally cooked food product. An important aspect of proper speed cooking is that the food product produced in a speed cook oven (in 1/7th to 1/10th the time in a conventional oven) is at or above the taste, appearance, quality and performance levels of the same food product cooked by conventional means. As this new and exciting technology is introduced into the market and becomes commercially and residentially available, the entire food industry will be re-energized and re-organized around new and different methods of food production, packaging, transportation, delivery, preparation and cooking of food products.
One reason the average family takes less time today to be together for meals is because the time required to prepare a complete meal, including the cooking time, is more time than most people are willing to invest. With quality speed cooking, cooking will become “just in time” or “on demand” as people will be able to cook foods 5 to 10 times faster than conventional cooking, and at quality levels equal to or higher than conventional cooking. The ability to custom cook, on demand, will revolutionize cooking, and food preparation. With this invention it is possible to short order cook exactly the food each person desires. Instead of “meatloaf tonight” it will be possible for one person to have steak, another chicken and another pork chops, because these food items can be cooked, from raw, together, in this speed cooking oven in a fraction of the time of conventional cooking. Or, for example picture an afternoon dinner party where fresh fish is laid out on a bed of ice. As guests approach the fresh fish selection, each can pick out a particular filet and watch as each filet is cooked perfectly in just a minute or two. Additionally, the person cooking the food will have the ability to control how well done the fish is cooked, the degree of browning on the outside (both top and bottom) and the inside temperature of the fish. If one person desires a salmon filet lightly done, this may take 1 minute while the next person may desire a well done filet which may, for example, only take an additional 20 seconds.
In addition to the speed advantage, this invention produces very high quality food products that are cooked perfectly-cooked the way the food product should be cooked instead of cooking using the conventional method. Historically, conventional cooking ovens heat to a predetermined temperature before the food product is inserted into the oven. Once the food product is inserted into the oven and over a period of time, the heat that has built up within the oven to a pre-heat temperature slowly conducts through the entire food product until there is overall heating of the interior of the food. This process is inefficient, but people have nevertheless developed the skill level necessary to overcome the inefficiencies of the method. With this invention food is cooked perfectly with less waste from boil off, cook off or other loss of food product due to the cooking process. As such, it will be possible to develop food products with fewer or less initial ingredients and still obtain the same final finished cooked food product. This invention therefore also relates to methods of food production wherein fewer ingredients are needed in order to attain the same final cooked product. Cooking with this new and novel method will allow food companies to reduce the quantity of the initial ingredients utilized for food preparation, but still maintain the final end product after the cooking process. Because this cooking process requires less initial starting ingredients (weight and volume) less packaging material is therefore required. Smaller package size leads to more space on the grocery shelves and in refrigeration coolers. Shipping costs, packaging costs, shelf space in grocery stores and many other areas of the food production system and delivery chain will be impacted as the world of food preparation, storage, transportation, delivery, preparation and sale moves from conventional cooking to speed cooking. In addition to the previously mentioned benefits, the ability to cook to gourmet standards with this invention will spawn an entire industry wherein gourmet signature chefs will be able to develop, brand and market their signature products for people to take home and enjoy without the cost or time expense of dining at a Five Star Restaurant. The speed cooking oven described herein will also be capable of internet connectivity. Information such as recipes, cook settings, special cooking instructions for gourmet food products can all be downloaded from the internet and imported directly into the cooking oven. Additionally, diagnostic tools will enable service providers to better predict future component breakdowns and also predict regular maintenance requirements, as remote monitoring of the oven will be possible.
Today there are a number of combination ovens sold for commercial use that cook in the range of two to three times faster than conventional. These ovens typically have an oven cavity roof or back wall launch of the microwave energy into the cooking cavity, with a simple convection flow of air that creates a gentle air flow pattern within the oven.
Fast cooking ovens in the 2 to 3 times speed range have also been developed. Compared to the higher speed hot air impingement flow speed cooking ovens, the more traditional microwave convection oven is a relatively simple rapid cook oven capable of cooking speeds of up to 3 times faster than conventional. These ovens utilize a convection blower motor and blower wheel mounted on the back wall (or side wall) with the oven air being drawn directly into the inlet and discharged from the blower wheel perimeter. A baffle plate isolates the blower discharge from the inlet and creates an outward flow of air along the oven cavity side, roof and floor walls, with the air flow turning back over the food and returning to the blower inlet. The baffle plate looks like a false back wall with gaps around the edges for air discharge and an opening in the center for air return and microwave energy in these ovens has been introduced from top, bottom, or the side walls. In general, these designs have a number of limitations and drawbacks. The first limitation is that the microwave launch system cannot equally illuminate multiple racks or pans of food. As a result, the efficiency of the microwave energy must be purposely reduced in order to avoid hot spots and poor cooking quality. Second, in a top (roof) launch or bottom (floor) launch microwave system, the cooking pans or other cooking vessels containing the food are situated directly above (in a bottom launch system) or directly below (in a top launch system) the microwave launch system which obscures the microwave energy from the pans further away from the microwave illumination source. To compensate for the non-uniform illumination of the microwaves within the oven cavity, the design of the oven microwave system is purposely limited in order to achieve uniformity. As a result, most traditional microwave convection ovens are actually single rack position rapid cook ovens. Many of these top or bottom launch systems require either a mode stirrer (a mechanical device to stir the microwave “e field”) or a turntable that rotates a platter or plate upon which the food rests (top launch system), or in some cases both a mode stirrer and a rotating tray is utilized. In addition to the microwave energy field non-uniformity, the convection air flow also has non-uniform behavior which results in lower air flow rates in the oven limiting the convection heat transfer rate, thereby limiting the cooking speed of the oven.
Generally, these oven designs direct the oven air flow down the side walls until the air flow reaches the oven cavity floor, then the air turns towards the back wall, flowing over the food product before returning back to the blower inlet and all the air returns to the blower inlet opening (usually located in the center of the back or side wall). The center pan often has a distinctive “V” cooking pattern near the blower inlet and this creates flow non-uniformity from the center rack position to the top/bottom positions. Balancing the air flow over several pans or cooking vessels is difficult as the air is drawn to the center of the back wall. As discussed herein, imparting high air flows to the oven in order to achieve high cook speeds results in non-uniform cooking. Usually, the discharge from a baffle plate is adjusted with air flow vanes or flow restrictions in order to achieve a more uniform flow state. The effectiveness of this approach is limited, and in general the oven air flow rates are maintained at modest rates.
In addition to the drawbacks described above relative to cooking speeds, these oven designs do not manage or handle air borne grease entrained by the convection air and by health code, these ovens must be operated under a hood when cooking meats or other grease laden foods. Information relevant to attempts to address these problems can be found in U.S. Pat. No. 4,337,384; U.S. Pat. No. 4,431,889; U.S. Pat. No. 5,166,487 and EP 0429822AJ. They have some speed advantage, but are not fast enough to radically change the cooking operation in a restaurant, commercial establishment or the home kitchen.
It has been found that, in order to create a break-through in the current cooking environment, cooking speeds greater than 5 times conventional cooking speeds must be achieved. A number of developments have taken place to create high speed commercial cooking ovens in the 3–10 times faster than conventional range, but fundamental drawbacks exist in these high speed commercial ovens and approaches. These ovens cook at high speed but some do not provide a quality finished food product. These ovens tend to be complex, unreliable and expensive to manufacture. As such, the finished sales price is high, thereby limiting the demand for, and commercial success of the ovens. Due to the state of the art of these high speed commercial cooking machines, the oven cavities tend to be small, they create smoke and odor, and therefore require expensive ventilation or catalytic clean-up. They are generally difficult to maintain, generally employ the use of a complex user interface with multiple control variables, and generally require large power supplies. They also tend to be less reliable due to the use of specialized components.
There have been different approaches to high speed cooking utilized in the past. One is impingement style air flow coupled with microwave, and another is convection style gas flow with microwave. Several high speed cooking ovens featuring impingement style convection flow fields coupled with microwave energy have been developed and impingement style heat transfer is not new in the art. As an example, impingement style heat transfer has been described in the General Electric Heat Transfer Data Book 1981 as “One method of producing relatively large forced convection heat transfer coefficients on a surface by gas (or other gases) is the use of a multiplicity of jets impinging upon the surface. As the gas jet approaches close to the surface it turns by an angle of 90 degrees, and thereby becomes what is called a “wall jet” (after the 90 degree turn). This type of impinging heat transfer has been studied extensively with predictive heat transfer relationships and the use of this impingement style cooking has historically been employed.
Some of the current oven designs feature opposed primary energy flows with impingement convection heat transfer being directed onto the upper surface of the food product (straight down at 90 degrees to the food product) and microwave energy launched from the floor of the oven cavity into the bottom of the food product. To provide bottom side convection heat transfer, the impingement air flow is pulled around the sides of the food product and across the bottom of the food via a low pressure gas return duct located directly below the food and has been described as a “shroud effect”. The flow beneath the food is accomplished using a ceramic platter with stand offs that have the dual purpose of supporting the food product and directing air flow along the bottom side of the food (as the standoffs are used to elevate the food thereby creating the air flow passage ways) with the air flow exiting downward via a series of apertures in the ceramic platter. The microwave energy is launched from below the food product and enters the food after passing through the ceramic platter, such ceramic platter is microwave transparent to allow the passage of the microwave energy through the platter and into the food product. While this approach produces high cooking speeds (5–10 times faster than conventional oven) it has several limitations as the ovens have non-uniform energy fluxes (convection and microwave) between the top and bottom of the food product thereby requiring complex control of the microwave and convection heating systems (sub-systems) to achieve speed cooking. In general, both the microwave energy and the convection energy flows are adjusted several times during the cooking cycle. The devices used to accomplish this adjustment are intensive blower motors and blower motor speed controllers, microwave power modulation, and a complex oven controller/user interface (needed to input multiple power and time settings for a given recipe). These devices are expensive and dramatically add to the complexity and cost of the final product. Additionally, these sub-systems tend to be unreliable, causing high service callouts. To achieve high speed the ovens require a relatively complex and expensive variable speed convection blower motor speed control with dynamically braking blower motor speed controllers and sophisticated electronic oven controls. The air blower must have variable speed capability in order to provide lower convective heat transfer rates when cooking more delicate food products such as cakes and other pastries. These ovens also have a lack of independent top side and bottom side convection (browning) heating because top impingement flow must wrap around the food product and flow under the food product in order to accomplish bottom side heating/browning. This requires the use of the previously mentioned expensive, fragile, and difficult to clean microwave transparent ceramic platter, which allows for the passage of microwaves. The ceramic platter must be configured with air flow channels in order to accomplish bottom side browning. The ceramic platter is expensive to manufacture, chips easily (creating health, performance and reliability problems) and requires regular cleaning, maintenance, and replacement. Because the ceramic platter is a necessary component, if a spare is not kept on hand, the oven is rendered inoperable in the event a platter is broken. Supply chains, stocks of inventory and additional money must be set aside in order to assure a constant supply of these ceramic platters. Indeed, ovens utilizing these ceramic platters have met with difficulty when introduced into commercial establishments with the prospective owners of these ovens constantly battling reliability problems and the need to re-supply their commercial establishments with ceramic platters. As an example of one problem, a chipped ceramic platter absorbs moisture, grease, oils and other by-products of the cooking process. As water, for example is absorbed within these platters, microwave performance decreases because the microwave energy interacts or couples with the water molecules (the principle of a microwave oven is the excitation of the oxygen-hydrogen bond within the water molecule) thereby reducing the microwave energy available for cooking. At some point, the overall oven heat will eventually, at least somewhat, dry a water soaked ceramic platter by boiling off the trapped water within the platter, but until this occurs, varying degrees of cooking performance may be experienced due to the varying moisture content within the platter. As more water is evaporated from the platter, more microwave energy is then available to couple with the food product instead of the water trapped within the platter. A food product cooked upon a water soaked platter will take longer to cook (or at least that portion of the cooking attributable to microwave energy) than the same food product cooked upon a dry platter. For this reason, a speed cooking oven requiring the use of a ceramic platter with apertures to both direct air flow and exhaust air flow is undesirable, but is nevertheless necessary as the described oven utilizes the “shroud” or “wrap” effect in order to fully and somewhat properly cook the food product; and the shroud effect is only created by the wrapping of the air around the food product via use of the ceramic platter. Also, with the requirement of very rapid air circulation through the oven (high velocity impingement), these ovens tend to be noisy. Cycling of these ovens from low velocity to high velocity generally produces a whirring noise not dissimilar to the sound of a jet engine winding up.
In these ovens, a uniform vertical jet flow field, over a range of flow rates, is needed for cooking over the entire cooking rack area. A common result of this requirement is that there is a lack of uniformity; so it is necessary to restrict or reduce the cooking zone to that area that experiences appropriate cooking, relative to the platter. This reduces the cooking capacity for a given oven cavity size because less of the platter can be cooked upon.
Especially lacking in these ovens is the ability to cook in the corner sections of the oven. With other technologies, means to overcome this problem are complex and have at least partially been solved by rotation of the food product under air jets with the use of a turntable. Using rotation (turntable) to compensate for jet non-uniformity also has the effect of reducing the useful cooking area of the appliance by at least approximately 25%. The circular turntable within either a square or rectangular oven cavity bottom does not take advantage of the cooking area located within the corners of the oven. In addition to the previously mentioned drawbacks of the ceramic platter, the platter further complicates the ability to achieve uniform flow conditions because the vertical jet air flow pattern couples to the ceramic platter which is being used to channel flow under the food. Additionally, the non-uniformity is a function of the shape and size of any cooking vessel used (e.g. pan, cookie sheet) because the air flow must wrap around the cooking vessel. In addition to the problems associated with these other oven cavity bottoms, the design and construction of the oven cavity top is complex given the need to add or modify the oven cavity roof for impingement nozzle plates/supply ducts. Also, modification of the oven cavity bottom is required for microwave launching, modification of the bottom and/or back wall is required for return gas ducts, and modification of the oven cavity top is required for the impingement style gas nozzles. Taken together, these modifications result in a small cook chamber section volume as compared to the entire oven cavity volume.
Another disadvantage in the previously described oven is that it is difficult to provide a microwave seal to the cavity floor (microwave launches through the oven floor through a circular waveguide) to prevent grease/liquid contamination of the wave guides. This is important because grease, water vapor or other particulate contamination of the microwave waveguide causes premature failure of the magnetron (tube) used to generate the microwave energy or “e-field” within the oven cavity. In these ovens, an opening in the oven cavity floor bottom allows the microwave launcher to extend up and through the oven cavity floor but the launcher must be sealed with a material that allows the passage of microwave energy, without any leakage of the seal because leakage of the seal then allows grease, food products and other by-products of the cooking process to contaminate the microwave launching system, thereby reducing the life of the microwave system, causing again, as described above, tube failure and service callouts.
Another disadvantage of the high speed ovens described above is that they require grease control because of the high velocity of the impinging air jets. This high velocity air impingement flow tends to entrain grease, both particles and vapor, into the convection gas, which speedly soils the oven cavity surfaces. One method of dealing with this grease load has been the use of a large catalyst to control the airborne grease. Drawbacks of the catalyst include its high cost and the catalyst tends to cause a pressure drop in the impingement air flow, thereby reducing operating efficiencies. The pressure drop is compensated by the use of a larger blower, thereby increasing component cost and lowering operating efficiencies and raising energy costs. The catalysts must be replaced periodically, adding both a service cost and an equipment cost to the oven.
Other technologies use a different impingement approach where vertical air jets are generated from the oven roof and floor simultaneously. The oven cavity bottom or floor impingement jets provide for bottom side cooking/browning while the oven cavity roof jets provide top side cooking and browning. In this device, the microwaves are launched from above the food product. Like the high velocity gas impingement air flow technology described above, this approach has several drawbacks.
First, the floor located gas nozzle plate and its supply duct are very difficult to maintain given their susceptibility to food spoils, spills and grease accumulation. To utilize the entire (or nearly) cooking area (rack), the top and bottom air jets must be very uniform in velocity or a non-uniform cooking and browning of the food product will result where the impingement jets produce circular brown spots on the food product surface. This polka dot browning effect is, of course generally not acceptable. Additionally, the requirement for very uniform gas flow to the food product adds complexity to the air flow system.
Second, uniform air jet fields are difficult to achieve at flows other than the design flow rates. When lower air flow rates (velocities) are needed, such as with pastries, it is difficult to attain proper air flow rates less than the design flow rate specified for higher air flows. Such reduced flows will minimize the effective cooking area within the oven cavity to a portion of the cavity where a reasonable flow field exits in order to cook a food product to an acceptable quality level. Alternatively, to compensate for the requirement of a less aggressive air flow, the convection flows must be greatly reduced, which will result in longer cook times (defeating the desire for a speed cooking oven).
Third, the general oven construction is complex, as the supply duct to the roof air plate must also act as a launch box for the microwaves. This requires that the roof jet plate be transparent to microwaves (e.g., ceramic plate with jet holes) so that the microwaves can be launched through the plate. Additionally, the floor ducts may become complex parts in the event they are designed to be removed for cleaning and/or servicing.
Fourth, having supply ducts on the floor and roof of the oven cavity greatly reduces the useful volume (cook section) of the oven because as much as half of the height of the oven cavity is occupied by these air channels. Other techniques have been used in an attempt to overcome these issues, but these techniques generally require more complexity such as oscillating nozzles, rotating food support, special food containers, and a smaller cook section and the work arounds tend to add complexity, cost and create other undesirable issues.
Finally, the previous approaches described for speed cooking ovens are suited for single rack cooking or single level cooking. Impingement style air flow is ineffective with two or more rack positions because one rack with food product will block air flow to the second or third rack.
During normal conventional cooking, metal pans, metal pots and metal sheet pans (and other metal products) are generally used, both commercially and residentially and the use of metal pans is widespread. It will be difficult for speed cooking ovens to become popular within either the commercial foodservice marketplace or within the residential market unless quality speed cooking utilizing metal pans can be accomplished.
Generally, speed cooking is slowed by the use of metal pans as microwave energy cannot penetrate and is deflected (re-distributed) within the oven cavity by the pans. Additionally, the metal pans completely block microwave energy when the energy is directed from below the pan on a single rack oven or in a top launch oven, the microwave energy is blocked from the lower pan by the top pan. It is therefore desirable that a speed cooking oven is capable of speed cooking, at high quality levels utilizing metal pans.
Another problem generally encountered is that browning of the lower surface of the food product is difficult to control because the method generally utilized for bottom side browning is conduction through a metal pan (pan is heated by radiant or microwave energy and then the thermal is transferred to the food product by direct contact with the food product) and this heating produces a griddle effect, thereby browning the bottom side of the food product. This method is difficult to control and generally produces an over brown or burned bottom surface of the food product. The ability to properly brown the bottom side of a food product, within a metal pan, is therefore important.
Accordingly, it is an object of the present invention to provide a method and apparatus for speed-cooking within a single-rack oven with an improved gas flow design capable of cooking most food products 5 to 10 times faster than conventional cooking.
It is another object of the present invention to provide such a speed cooking oven which utilizes a gas flow pattern that averages out the maximum and the minimum gas flow variation for a given point in the oven cook section resulting in a gas flow that is averaged spatially over the food product surface.
It is also an object to provide such a speed-cooking oven that produces uniform low flow conditions required for high quality baking.
A further object is to provide such a speed-cooking oven with a continuous floor that is not interrupted by gas ducts or microwave launching and/or other systems and is easy for the user to clean and maintain.
Another object is to provide a means to produce and direct various gas flow patterns in the oven that either reduce or enhance the convection heat transfer coefficient to the product.
It is another object to provide a relatively constant flow through the oven which eliminates the need for varying the air flow thereby improving grease extraction by maintaining higher flow rates through-out the cooking cycle regardless of the required heat transfer to the product.
Another object is to provide such an oven with a simplified oven construction, eliminating the need for variable speed impingement air blowers, dynamically braking blower motor speed controllers and associated electronics.
Still another object is to provide a speed cooking oven that is capable of high quality speed cooking within metal pans, pots, sheet pans and other metal cooking devices found in residential and commercial kitchens.
Another object is to provide a speed cooking oven that is capable of performing bottom side browning of the food product utilizing gas flow to the bottom surface of the food product without the use of floor mounted air plates.
Another object is to provide such a speed-cooking oven that increases the useful oven cook section height by eliminating ducts and/or jet plates from the floor of the oven.
Another object is to provide such an oven with a gas flow field where grease entrainment is reduced by eliminating the vertical impingement style flow that tends to throw or kick grease into the gas stream from both the cooking pan and the food product, while achieving sufficiently high heat transfer rates.
Another object is to provide such an oven that matches the general microwave and convection heat transfer energy patterns, such that uniform cooking conditions can be achieved on the top side and bottom side of the food product.
Another object is to provide such an oven with gas deflection means that allows flexibility of gas diversion throughout the speed cooking oven.
It is a further object to provide such an oven for speed cooking on multiple racks.
It is a further object to provide such an oven which is more cost effective to manufacture and easier to clean and maintain.
Yet another object is to provide such an oven which is more reliable due to improvements and simplifications in component sub-systems.
Other objectives, features and advantages will be apparent in the written description which follows.